Approaching $x=-6$ from the left, you will approach -2, even though the function is undefined at $x=6$. Likewise, approaching $x=-6$ from the right, you will approach 2.

The meaning of "approaching" in this case is pretty intuitive, as the function doesn't change value on each side of $x=6$. For a more rigorous definition of what "approaching" means in the general case, read about the epsilon-delta definition of limit.